In order to separate such a mixture of magnetizable and non-magnetizable particles, some methods are already known in the prior art and will be presented here in brief. Basically, such methods are based on the magnetic force which acts on the magnetizable particles when there is a magnetic field gradient.
On the one hand batch methods are known, in which magnetizable separating bodies such as iron wires or fibers or iron plates having surface structures such as grooves, studs, etc. in an external magnetic field generate a strong field gradient in their vicinity, which fixes the magnetic particles of a suspension flowing past in a separation phase. In a second phase, the magnetic fraction thus concentrated is suspended in a subsequent flushing step with the magnetic field switched off. Disadvantageously, this method is discontinuous and requires the flushing step.
Continuous methods are effectively known only using disadvantageous mechanically moved parts, in particular even for sizeable magnetizable particles, in which for example a magnet generates a magnetic field gradient on a surface of a rotating hollow cylinder, a disk or a conveyor belt. Owing to this movement, the surface travels out of the magnetic field so that the magnetizable fraction then falls off or is stripped off. An example of this is the separation of iron from scrap. Another disadvantage of these methods is the small permissible distances between the magnet and the separating surface.
It has recently been proposed, by means of a plane or cylindrical magnetic field generation means, to use a gradient field which deflects magnetizable particles to at least one surface of a separating channel, so that magnetizable particles in a suspension flowing parallel to the magnetic field generation means in the separating channel are attracted and describe a path closer to the magnetic field generation means. At the output, separated non-magnetic and magnetic material flows are then intended to flow out through baffles.
This approach, however, has disadvantages in several regards. Specifically, the magnetic field and therefore also the magnetic force are intrinsically greater in the direction of the magnetic field generation means, so that particles far away from the magnetic field generation means are deflected less, while particles close to the magnetic field generation means are magnetically fixed on the surface even against the hydrodynamic forces of the flow. The separating effect is therefore reduced, and on the other hand here again a flushing step must be used for extracting the magnetic fraction after switching off the magnetic field.